Preparation Method for Ethylene-Vinyl Alcohol Copolymer

Abstract

The present disclosure relates to a method for preparing an ethylene-vinyl alcohol copolymer capable of efficiently obtaining the ethylene-vinyl alcohol copolymer. Specifically, as the present disclosure performs a supercritical extraction process after saponifying an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst, it is possible to minimize the generation of waste liquid and effectively remove by-products such as catalyst residues without complicated equipment such as a multi-stage distillation column, or a pipe mixer and a water tank, and thus an ethylene-vinyl alcohol copolymer can be efficiently obtained.

1 . A method for preparing an ethylene-vinyl alcohol copolymer, comprising:
 performing a saponification reaction of reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst in an alcohol solvent to produce an ethylene-vinyl alcohol copolymer; and   extracting the alcohol solvent contained in a saponification reaction product under a supercritical carbon dioxide condition;   wherein in the supercritical carbon dioxide condition, CO2 has a pressure of 80 bar or more to 150 bar or less, and a temperature of 40° C. or more to 60° C. or less.   
     
     
         2 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein the saponification reaction is performed by adding a solution of the alkali catalyst dropwise to the ethylene-vinyl acetate copolymer dispersed in the alcohol solvent to react. 
     
     
         3 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein the alcohol solvent is at least one selected from the group consisting of methanol, ethanol, propanol, isopropanol, and butanol. 
     
     
         4 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein the alkali catalyst is lithium hydroxide, sodium hydroxide, or potassium hydroxide. 
     
     
         5 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein a total amount of the alkali catalyst used is 0.01 mole or more to less than 0.03 moles based on 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer. 
     
     
         6 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein a temperature of the saponification reaction is 40° C. or more to 120° C. or less. 
     
     
         7 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein a pressure of the saponification reaction is 1 bar or more to 5 bar or less. 
     
     
         8 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , further comprising a step of gelling or solidifying a resultant containing the ethylene-vinyl alcohol copolymer from the saponification reaction before the extracting step. 
     
     
         9 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein in the supercritical carbon dioxide condition, CO2 has a pressure of 100 bar or more to 150 bar or less, and a temperature of 40° C. or more to 50° C. or less. 
     
     
         10 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein a product containing the ethylene-vinyl alcohol copolymer obtained after the extracting step has the alcohol solvent in an amount of 15 wt % or less based on a total weight of the product. 
     
     
         11 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , further comprising a step of immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing a carboxylic acid, and then drying, after the extracting step. 
     
     
         12 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein the saponification reaction comprises a first saponification reaction step of adding a first alkali catalyst dropwise to the ethylene-vinyl acetate copolymer dispersed in an alcohol solvent; and a second saponification reaction step of adding a second alkali catalyst dropwise to a reaction mixture from the first saponification. 
     
     
         13 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 1 , wherein the alcohol solvent is used in an amount of 100 parts by weight to 1000 parts by weight, based on 100 parts by weight of the ethylene-vinyl acetate copolymer. 
     
     
         14 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 2 , wherein the solution of the alkali catalyst is added dropwise so that an amount of the alkali catalyst added per minute is 1.0*10 −5  mole to 13*10 −5  moles based on 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer. 
     
     
         15 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 8 , wherein the gelation or solidification is performed by cooling to about −10° C. or more to about 5° C. or less. 
     
     
         16 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 11 , wherein the carboxylic acid comprises acetic acid. 
     
     
         17 . The method for preparing an ethylene-vinyl alcohol copolymer of  claim 11 , wherein a concentration of the aqueous solution containing carboxylic acid is 0.01 wt % to 1 wt %.